When a fiber optic cable is interfaced to a semiconductor device special care must be taken if the amount of loss of the transmitted light is to be minimized. An angular misalignment between the cable and the device, as shown in FIG. 1A, may cause a loss of transmitted light. Losses in transmission may also occur if the fiber optic cable is axially misaligned with the semiconductor device as shown in FIG. 1B. Additionally, Fresnel losses may occur due to reflection if the transmitted light must pass between materials having different indices of refraction. For example, light transmitted from the semiconductor device to the fiber optic cable might pass through an epoxy layer on the device and through an air gap between the semiconductor device and the cable. The Fresnel loss may be calculated as: ##EQU1## wherein T represents the transmissivity between two media having indices of refraction n1 and n2. If a gallium arsenide phosphide (GaASp) semiconductor device is used, the index of refraction (n) for GaAsP is 3.6; for clear epoxy, n is 1.5; and, for a fiber optic cable, n is 1.5. Thus, the loss in transmission for this exemplary case, can reach approximately 1.2 dB. In addition to the Fresnel losses the amount of axial separation between the cable and the semiconductor device (shown in FIG. 1C) also contributes some loss.
One prior art approach to minimizing light loss, shown in FIG. 2A, is to make the fiber optic cable an integral part of the semiconductor device. Such a semiconductor/cable combination, generally referred to as a "pig-tail," is clamped in place within a housing. This prior art approach promotes proper alignment and minimal Fresnel losses. The main disadvantage with "pig-tail" devices is the fragility due to having a delicate cable protrude from an equally delicate semiconductor device which necessitates special handling and greatly inhibits mechanical design flexibility.
An additional prior art device of the pig-tail type is shown in FIGS. 2B and 2C. A fiber optic cable is made to abut a semiconductor device and the combination is epoxied to form an integral unit. In this way Fresnel losses are minimized. However, losses due to mechanical misalignment during the epoxying process can still occur unless stringent alignment controls are enforced.
Another prior art approach is to use a screw-type mechanical connector to interface the cable with the semiconductor device. Typical connectors are shown in FIGS. 2D, 2E, and 2F. Because the cable must be screwed into a connector, cable connection is difficult, especially if space is limited. Further, a partial separation at the semiconductor/cable interface, and the resultant loss in light, may be hidden by the connector and may exist for a period of time before it is found and corrected.